This invention relates to spectroscopic in-situ analysis of constituents in a chemical reaction. More particularly, this invention relates to spectroscopic insitu analysis of constituents in a slurry loop polymerization reactor.
Spectroscopic analysis is a branch of analytical chemistry devoted to identification of elements and elucidation of atomic and molecular structure. Generally, the identification of elements and elucidation of atomic and molecular structure is accomplished by illuminating or irradiating the substance under examination and then measuring the radiant energy absorbed or emitted by the substance. The energy absorbed or emitted may be in any of the wavelengths of the electromagnetic spectrum. By comparing and/or correlating the measured wavelengths absorbed or emitted by the sample with wavelengths emitted or absorbed from known elements or molecules, information about a sample may be determined.
More particularly, spectroscopic analysis generally requires isolating a portion of the substance under investigation. The isolated portion is then prepared for illuminating or irradiating by an energy source. After irradiation, the energy absorbed or emitted by the isolated portion is measured and correlated to values derived from known materials measured under similar conditions.
Spectroscopic analysis is a common tool used in laboratories and industrial processes. Its uses include determining the molecular identity and properties of a chemical composition as well as monitoring the progress of a reaction. Whether conducting a laboratory exercise or industrial process, this type of information is desirable. This is so because, for example, data derived from spectroscopic analysis may be used to identify the final product of these reactions and determine the consumption and/or identity of intermediates produced at selected stages in a multistage process.
For industrial processes and particularly industrial chemical reactions, in-situ identification and monitoring of (i) the reaction constituents, (ii) the reaction intermediates, (iii) the consumption rate of the starting materials, and (iv) the final product are desirable. In-situ analysis is desirable generally because the analysis environment is the reaction environment within the reaction vessel. In this way, the isolation and preparation of a portion of the substance under investigation prior to irradiation is avoided. And still more desirable is the acquisition and assimilation of analysis information after the passage of a relatively short period of time from the moment the analysis process is initiated, otherwise referred to as xe2x80x9creal time analysisxe2x80x9d.
However, there remain many industrial processes, and particularly industrial chemical reaction environments, for which spectroscopic analysis techniques do not offer an investigator the option of conducting reliable, in-situ, real time analysis. As such, there exists a need for further development in the field of in-situ, real time spectroscopic analysis and the application thereof in industrial processes.
The present invention provides both apparatus and methods for conducting in-situ, real time spectroscopic analysis of one or more reaction constituents present in a reactor, particularly a slurry olefin polymerization reactor and more particularly, a slurry loop olefin polymerization reactor. Examples of reaction constituents include polymerized and polymerizable olefins. Examples of polymerized olefins include, but are not limited to polypropylene, polyethylene, polyisobutylene, and homopolymers and copolymers thereof. Other examples of reactor constituents include, but are not limited to hydrogen, propane, ethane, butane monomers, and comonomers. Examples of monomers and comonomers include, but are not limited to ethylene, propylene, butene, hexene, octene, isobutylene, styrene, norbornene and the like.
Without limiting the present invention to any particular spectroscopic analysis technique, the inventors have observed in a slurry reaction environment a correlation between in-situ collected Raman spectra (a product of Raman spectroscopy) from the liquid phase of the reaction environment and the concentration of at least one reactor constituent. Furthermore, the inventors have discovered that this correlation, in combination with in-situ, real time analysis of at least one reactor constituent in such a reactor will allow for improved control of the final product properties, such as melt flow rate. Improved control of the final product properties is achieved by metering the flow of at least one reactor constituent into the slurry reactor in response to the in-situ measured concentration of at least one reactor constituent.
In one embodiment, a method of olefin polymerization in a reactor having reactor constituents in a liquid phase is provided. The method steps include measuring in-situ a first reactor constituent and metering the flow of a second reactor constituent into the reactor in response to the measuring step. The first and second reactor constituents may be the same constituent or they may be different constituents.
In another embodiment, another method of olefin polymerization in a multi-phase reactor containing reactor constituents is provided. The method steps include irradiating in-situ the reactor constituents, measuring scattered or reflected energy from the irradiated reactor constituents, determining from the measured scattered or reflected energy a concentration of at least one reactor constituent, and metering the flow of at least one reactor constituent into the reactor in response to the determining step.
In another embodiment, a method of olefin polymerization in a reactor containing reactor constituents in a liquid phase is provided. These method steps include irradiating in-situ the liquid phase, measuring the frequencies scattered or reflected by the irradiated liquid phase, correlating at least one measured frequency with the concentration of a first reactor constituent, and metering, in response to the correlating step, a flow of the first reactor constituent into the reactor.
In another embodiment, another method of producing a polyolefin in a reactor containing reactor constituents in a liquid phase is provided. These method steps include irradiating in-situ the liquid phase, measuring the frequencies scattered by the irradiated liquid phase, determining from the measured frequencies a concentration of one or more reactor constituents, comparing the concentration of one or more reactor constituents with one or more values that correlate to one or more selected physical properties of the polyolefin, and metering, in response to the correlating step, the flow of one or more reactor constituents into the reactor. One of the selected physical properties of the polyolefin may be melt flow rate. Additionally, the metered flow of one or more reactor constituents into the reactor may be controlled such that the polyolefin produced may be defined, in part, by a melt flow rate value within a selected melt flow rate range.
In another embodiment, a method of olefin polymerization in a slurry reactor containing reactor constituents, including hydrogen, in a liquid phase is provided. These method steps include, irradiating in-situ the liquid phase, measuring the frequency scattered or reflected by the hydrogen in the liquid phase, determining the concentration of hydrogen in the liquid phase from the measured frequency, and metering, in response to the concentration of hydrogen measured, the flow of the hydrogen into the reactor.